One of the more promising near-term applications for superconducting thin films is in the area of passive microwave devices such as delay lines, resonators, antennas, and filters. Unlike applications involving junctions or weak links which involve relatively small coated areas, microwave devices require coating sizes of at least a few square centimeters with more complex designs requiring coated areas of ten square centimeters or more. Additionally, two-sided coatings are often desired for some applications.
Numerous techniques have been used to deposit superconducting thin films, but the highest quality films have been produced by in situ processes employing sputtering or pulsed laser deposition. Optimum superconducting performance by the superconducting films is obtained when such films are highly crystalline. This requires uniform and accurate heating of the substrate, e.g., heating in the vicinity of 800.degree. C. for YBCO films.
The previously known substrate heaters have suffered from several deficiencies including, e.g., formation of tooling marks upon the deposited films from the support of the substrate during the deposition, temperature gradients across the substrate from the use of multiple lamp type heating elements, evaporation and subsequent contamination of the substrate from the sides of the substrate holder, and difficulties in loading a substrate into the heater. Additionally, in order to obtain two sided coatings, it is not possible to attach the substrate to a substrate holder, e.g., by use of silver paint, without degrading the quality of the film composition and the surface of one side.
It is an object of the present invention to provide a substrate heater having uniform heating of the substrate during a deposition of a thin film at high temperatures.
It is a further object of the invention to provide a substrate heater which leaves no tooling marks from the mounting fixture in the finished thin film coating.
It is a still further object of this invention to provide a substrate heater for coating both sides of a disk that eliminates the usage of any paint or paste for attachment to a substrate block or platform.
It is a still further object of the invention to provide a substrate heater with reduced contamination of the finished thin film coating from evaporation of the sides of the substrate heater.